Liquid crystal displays have been recently replacing traditional CRTs in applications like computer monitors and TVs. A liquid crystal display includes a glass cell as a light valve and a back light module as a light source. Back light modules usually comprise cold cathode fluorescent lamps and light directors. After light is emitted from the back light modules, it may be polarized first in order to be controlled by the aligned liquid crystals in the liquid crystal cell. Therefore, a first polarizer may be attached at the rear side of the glass cell and a second polarizer attached at the front side of the glass cell for controlling light emission in a transmission type liquid crystal display. After light goes through the first polarizer, at least half of the light energy would be blocked and can not contribute to the display. Therefore, several other display technologies have been developed to eliminate the use of polarizers.
Recently, light emitting diode-based displays have become a promising light source for displays. For example, light emitting diodes (LED) can be the light source of a projective type display. FIG. 7 shows a projective type display having LED array chips as its light source. The projective type display includes three single-colored LED array substrates 1R, 1G, and 1B, a dichroic lens 2, a projection lens 3, and a screen 4. Red light from red-colored LED substrate 1R, green light from green-colored LED substrate 1G, and blue light from blue-colored LED substrate 1B are mixed at dichroic lens 2 and are projected to the screen 2 via projection lens 3. Each substrate comprises only single-colored LED chips. An instance of such a substrate 1 is shown in FIG. 8. In this display, no liquid crystal panels or polarizers are needed, so light energy efficiency is improved as compared to the traditional liquid crystal display. But there is a need to integrate three-colored LED chips into one substrate to reduce the cost of light sources.